This invention relates generally to remote controlled travel apparatus, and in particular to such apparatus that includes a track guided vehicle automatically controlled in its travel between positions along the track. The apparatus is applicable as part of a warehouse stock stacking and retrieval system, and it will be convenient to hereinafter disclose the invention in relation to that exemplary application. It should be appreciated, however, that the apparatus is not limited to that application.
A number of shelf servicing transportation systems have been developed and installed in warehouses for stocking and retrieving shelf stock. These systems generally include a vehicle mounted between upper and lower guide tracks extending along shelving aisles or corridors, for running along the tracks to stack stock onto the shelving and retrieve the stock therefrom as necessary.
Initially, travel of the vehicle and stock stacking retrieval operations were controlled manually in the sense that an operator usually travelled with the vehicle manually operating controls carried on the vehicle. More recently, however, those vehicles have become remotely controlled, with a single operator positioned at a distant control station and initiating travel and operating command signals to one or more unmanned vehicles.
The command signals to the vehicles are generally Provided through a computer based control system which, inter alia, monitors the actual vehicle position and travel within the warehouse. In that regard, it is important for the system to know and monitor the vehicle's position to determine where it must travel to stack and/or retrieve stock in response to given command signals. That has been achieved by using the guide track as a measured reference grid and moving the vehicle along the track a predetermined distance to shift the vehicle from one reference grid point to another point. With stock shelves each having separate known grid points it becomes possible for the vehicle to travel to and from shelves for stock stacking and/or retrieval.
Various arrangements have been developed for measuring the distance a vehicle is required to travel between points. They include odometer means which count revolutions of the vehicle wheels and relate that to the distance travelled, and flag means strategically placed about the grid which are triggered by the passing vehicle to signal its presence which again can be related back to the distance travelled by the vehicles. These arrangements have not been found to be particularly accurate or efficient. In that regard, the odometer means tends to become progressively inaccurate with distance travelled through wheel rotation aberrations, particularly wheel spin and skid, which inaccuracies tend to compound through successive vehicle movements. Depending on the extensiveness of placement, the flag means may only provide an approximate indication of vehicle position and distance travelled so that accurate monitoring is difficult. In any event, flag means is prone to failure or damage thereby reducing its effectiveness.